In an electrochemical gas sensor for a gas to be measured, for example, oxygen in the air, each arriving oxygen molecule is reacted electrochemically at a measuring electrode. To limit the signal current, the supply of oxygen is reduced by permeation through closed membranes or by diffusion through capillaries, or the electrochemical reaction takes place at so-called microelectrodes. The manufacture of microelectrodes is expensive because the participation of the electrical contacts or contacting in the electrochemical reaction must be ruled out or the electrochemically active measuring electrode surface must not change in terms of its size in order to ensure that reproducible measured values are obtained.
The manufacture of such microelectrodes is carried out, for example, by embedding a wire in a synthetic resin or fusion in glass or even by etching or growth techniques.
Examples of such microelectrodes can be found in EP 0 266 432 B1. However, even oxygen sensors equipped with membranes or capillaries still yield undesiredly high signal currents of about 200 μA during the admission of air, which leads to the need to increase the battery capacity in portable gas-measuring devices in order to obtain the long service life desired.
Furthermore, closed membranes and long capillaries lead to an undesired prolongation of the response time.